In 1913 she became a corresponding secretary of the International Woman Suffrage Alliance (IWSA). Schwimmer toured Europe with Carrie Chapman Catt to lecture on female suffrage. She also edited the magazine A nő (The Woman).[2] In 1914 Schwimmer moved to London and worked as a correspondent of various European newspapers and press secretary for IWSA.[3] When World War I broke out, she could not return home and began to agitate for the end of hostilities. In 1914 she toured the USA to demand that president Woodrow Wilson form a neutral conference to end the war. In 1915 she took part in the formation of the Woman's Peace Party.

When Hungary gained independence from Austria-Hungary in 1918, prime minister Mihály Károlyi appointed Schwimmer to be ambassador to Switzerland. When the communists gained control of the government in 1919, she opposed them and lost her civil rights. In 1920, when Miklós Horthy's government ousted the communists, she fled to Vienna and in 1921 to the USA. She settled in Chicago and did not move back to Hungary, where she had contributed to building the foundation for future women in Hungarian politics.

Due to her pacifist beliefs, Schwimmer was labeled as a socialist in the USA. She spent most of her remaining life fighting slander against her person. When Fred Marvin accused her of being a German spy and a Bolshevist agent, she sued and received $17,000 in damages. However, she could not gain US citizenship because of her pacifism—the U.S. Supreme Court ruled against her in United States v. Schwimmer (1929). In 1946, United States v. Schwimmer was overturned in Girouard v. United States. She spent the rest of her life in the country as a stateless person.